Electrical resistance



H. M. WALMSLEY ELECTRIAL RESISTANCE Aug 12 1924.

Filed Nov. 13, 1922 Ma! mgu z 351 f? aim W4 I Patented Aug. 12, 1924.

UNITED STATES 1,505,072 PATENT OFFICE.

HAROLD M. WALMSLEY, OF NORt-VOOD, OHIO, ASSIGNOR TO VJILLIALM H. KELLER, OF NORTON, VIRGINIA.

ELECTRICAL RESISTANCE.

Application filed November 13, 1922. Serial No. 600,582.

To all whom it may concern:

Be it known that I, HAROLD M. amas- LEY, a citizen of the United States of Amen ica, residing at Norwood, county of Hamil- 5 ton, and State of Ohio, have invented new and useful Improvements in Electrical Resistances, of which the following is a speci fication.

This invention relates to devices for inserting resistance in electric circuits whereby control of the current flowing in such circuits may be effected for various purposes.

The invention particularly relates to that type of resistance element known as a grid and more especially to grids which are punched from sheet steel or other metal. It is to be understood, however, that the invention is not limited to the applications 2 mentioned.

One of the principal objects of the invention is to improve the ventilation.

A further object of the invention is 10 provide a structure of grid giving a higher resistance for a given area of metal in the grid.

A further object of the invention is to so dispose the material of the grid that it. may be mechanically strengthened against 1H) warpage or buckling.

A further object of the invent-ion is to provide a desired distribution of temperature in the grid.

Other and ancillary objects will appear hereinafter.

In the accompanying drawings which illustrate the invention:

Fig. l is a side view of a rheostat containing resistance which embodies the invention; and

Fig. 2 is a section on the line 22 of Fig. 1 on an enlarged scale.

Referring to thedrawings the frame in which the grids are to be mounted comprise the end plates at and 6 between which extend the clamping bolts 0, d and 0 having nuts outside the ends of the plates as shown. Between the: plates are arranged the grids f.

The structure of the grid is shown best in Fig. 2 from which it appears that each grid comprises the refleXed portions or legs 1, 2, 3, 4;, 5 and 6, thus providing a tortuone path for the current in going from one side or end of the grid to the other. At one end of each of the outside bars of the grid is a hole, through which the bolt-s 0 and (Z pass, while at the middle of the grid upon the opposite side from the holes mentioned, is another hole through which is threaded the bolt 6. The grids are ordinarily insulated from the bolts d, c and e by insulating sleeves or bushings as 7, 8 and 9 which envelop the bolts. The grids are spaced from each other on the clamping bolts by means of washers. These washers as 10, 11, 12 and 13 may be of insulating material, it being desired to insulate adjacent grids from-each other at these points, while washers, as 14, 15, 16 and 17 may be of metal, it being desired to electrically connect the adjacent grids at these points. Where desired the metal washers may be extended into terminals as 18 and 19 for receiving the ends of the wires, by which external connections are to be made. Pref erably the insulating bushings and washers referred to are made of mica, although other insulating material might be employed.

In order to insure that the grids are properly spaced apart, and without necessitating an undue magnitude of the clamping bolts, rods 20, 21, 22 and 23 are passed through holes in the grids at their points of fle-Xure. These rods are insulated from the grids by insulating bushings 24, 25, 26, and 27 and carry insulating washers as 28, 29, 30 and 31 interposed between the grids. These rods 20, 21, 22 and 23 are much smaller than the clamping rods. They serve to support the insulating washers which separate the grids, and ordinarily have slight, if any, clamping effect. They may be held in position by being extended through the end plates outside of which nuts as 32 and 33 may be applied to them.

Each grid may be punched from sheet steel and it is to be observed that instead of the legs 1, 2, 3, i, 5 and 6 being parallel to each other as was the case with older types of grids, adjacent legs converge towards each other in one direct-ion and diverge from each other in the other direction, the end of one leg at the end where it is most divergent from its adjacent leg upon one side converging into a junction with the adjacent leg upon the other side. Thus the leg 3 (see Fig. 2) at its lower end diverges the most from the leg 2 upon one side while this same lower end converges to and joins with the leg 4 upon the opposite side or, taking the upper end of the leg 3, this converges to and is joined with the leg 2 and has the greatest divergence from the leg 4. This arrangement of having the pairs of grid legs converging at one end and diverging at the other provides larger area of air spaces between the grids whereby the ventilation is improved and also the resistance of the grid over the old type is increased for a given area of steel by in creasing the length of the effective resistance path of the current through the grid or conversely the same resistance may be obtained with a less area of steel.

It is also tobe observed that the outer legs of the grid 1 and 6 are of less width than the intermediate legs 2 and 5 which in turn are of less width than the inside legs 3 and l, the grid being of uniform thickness (that of the plate from which it is punched), the cross sections and consequently the resistances of the legs are proportional to the widths of the legs. It therefore follows that the cross section of each of the legs 3 and a, and therefore their current carrying capacity is greater and resistance less than the legs 2 and 5 which have geater current carrying capacity and less resistance than the legs 1 andG. This has the important result that the greatest resistance and consequently the greatest'heat generated is in the outer legs 1 and 6 which have the best opportunity for heat dissipation. The legs 2 and 5 Which has less opportunity for heat dissipation are next in resistance and heat generation, while the innermost legs 3 and l have the least opportunity for heat dissipation and have the least resistance and generate the least heat. Each part of the grid may therefore be made to play its proper part according to its situation by the proportioning of resistance and dissipation of heat so that all parts of the grid may be eiliciently utilized. By relatively proportioning the legs according to the circumstances and materials used, all of the legs of the grid may be made to heat uniformly so that warping and buckling, due to unequal heating may be avoided. Furthermore, even if there is unequal heating the tendency to greatest heating is usually in the middle legs so'that they are most liable to warping or weakening by the greater heat, but it will be observed that in the present case the inner grids are of greatest cross section and therefore stronger to resist distortion than the outer ones which, as above pointed out, are of smaller cross section and therefore of less mechanical strength.

From the foregoing it is believed that it will appear that this present invention provides a new form of grid having improved ventilation, and enlarged current carrying capacity and resistance for a given amount of'm'aterial and wherein the material is so distributed as to provide mechanical strength at the points subjected to greatest stresses and reducing the material at points where the stresses are reduced and that a mechanically strong structure is provided with a minimum of material, and further the heat is so distributed that the stresses tend ing to warp or buckle the grid are reduced.

While the invention has been illustrated in what is considered its best application it may have other embodiments without departing from its spirit and is not therefore limited to the structure shown in the drawings.

What I claim is:

1. An electrical resistance grid having interior legs of greater cross section than legs located exteriorly thereof.

2. An electrical resistance grid having legs of different cross sections, the innermost legs having the greatest cross section and the outermost legs having the least cross section and intermediately located legs having cross sections of sizes intermediate those of the said innermost and outermost legs.

9 legs converging toward each other throughout the greater portion of their length.

4t. An electrical resistance grid having legs straight throughout the greater portion of their length, said straight portions converging toward each other.

5. An electrical resistance grid having legs converging toward each other throughout the greater portion of their length, ad jacentlegs meeting at one end and being widest divergent at the other end, and each of said legs at one end meeting with the ad jacent leg upon one side and being most di vergent from the adjacent leg upon the other side.

'6. An electrical resistance grid of substantia-lly uniform thickness having interior legs of greater width than legs located e'xteriorly thereof.

7. An electrical resistance grid of substantially uniform thickness having legs converging toward each other throughout the greater portion of their length.

8. An electrical resistance grid having interior legs of greater cross section than legs located exteriorly thereof and having adja-- cent legs converging toward each other throughout the greater portion of their length.

9. An electrical resistance grid punched from a sheet of metal and having interior legs of greater width than legs located ex teriorly thereof and said legs being substantially straight throughout the greater por- 'tion of their length, the straight portions of adjacent legs convergingtoward. each other in one direction and diverging from each other in the other direction, adjacent legs meeting at one end and being widest divergent at the other end and each of said legs at 0. An electrical resistance grid having llt) one end meeting With the adjacent leg upon one side and being most divergent from the adjacent leg upon the other side.

10. An electrical resistance grid having 5 legs of different resistance and heat genera tion, the heat generation being so distributed as to produce substantially uniform temperature throughout the grid.

11. An electrical resistance grid having its heat generation properties distributed in a predetermined manner to produce desired temperatures at different portions of the rid.

c In testimony whereof I have signed this specification this 31st day of October, 1922 H. M. l/VALMSLEY. 

